Determination of 234U/238U ratio: comparison of multi-collector ICPMS and ICP-QMS for water, hair and nails samples, and comparison with alpha-spectrometry for water samples

The (234)U/(238)U ratio in water, hair and nails samples was determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) and inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and by alpha-spectrometry for the water samples only. A correlation of 0.99 was found between the two ICPMS methods and of 0.98 with alpha-spectrometry. The range of activity ratios was between 0.9 and 2.6 according to the MC-ICPMS measurements. The reproducibility of both ICPMS techniques was better than 4% for water samples containing 1 mug l(-1) of uranium and a (234)U/(238)U atom ratio of 54.9 x 10(-6). Sample preparation for the ICPMS consisted of dilution of water samples containing >10 microg l(-1) of uranium and measurement time was approximately 1 min, while alpha-spectrometry involved pre-concentration and separation of the uranium and counting times of 1,000 min.     

Assessment of uranium exposure from total activity and 234U:238U activity ratios in urine

Radiation workers at Atomic Weapons Establishment (AWE) are monitored for uranium exposure by routine bioassay sampling (primarily urine sampling). However, the interpretation of uranium in urine and faecal results in terms of occupational intakes is difficult because of the presence of uranium due to intakes from environmental (dietary) sources. For uranium in urine data obtained using current analytical techniques at AWE, the mean, median and standard deviation of excreted uranium concentrations were 0.006, 0.002 and 0.012 μg per g creatinine, respectively. These values are consistent with what might be expected from local dietary intakes and the knowledge that occupational exposures at AWE are likely to be very low. However, some samples do exceed derived investigation levels (DILs), which have been set up taking account of the likely contribution from environmental sources. We investigate how the activity and isotopic composition of uranium in the diet affects the sensitivity of uranium in urine monitoring for occupational exposures. We conclude that DILs based on both total uranium in urine activity and also (234)U:(238)U ratios are useful given the likely variation in dietary contribution for AWE workers. Assuming a background excretion rate and that the enrichment of the likely exposure is known, it is possible to assess exposures using (234)U:(238)U ratios and/or total uranium activity. The health implications of internalised uranium, enriched to <5-8 % by mass (235)U, centre on its nephrotoxicity; the DILs for bioassay samples at AWE are an order of magnitude below the conservative recommendations made by the literature.     

Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters

Kinetics of dissolution of (238)U, (234)U and (230)Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultrafiltrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolní Rozínka' at Rozná, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h(-1) and the sampling period is typically 1 month. Studied filters contained 125 +/- 6 mBq (238)U in equilibrium with (234)U and (230)Th; no (232)Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for (238)U and (234)U and slow dissolution half-times of 173 and 116 d were found for (238)U and (234)U, respectively. No detectable dissolution of (230)Th was found.     

Mass spectrometric study of GaInPAsSb/GaSb heterostructures

The composition and thickness of GaInPAsSb five-component layers grown on GaSb substrates by temperature-gradient liquid phase crystallization and liquid phase epitaxy and the heterojunction width have been determined by secondary neutral mass spectrometry. The heterostructures have been compared from the viewpoint of technological applications.     

Mass spectrometric determination of O-glycosylation sites using beta-elimination and partial acid hydrolysis

The present study demonstrates that treating O-glycosylated peptides with methylamine vapor followed by partial acid hydrolysis is an effective means for locating O-glycosylation site(s). The reaction with methylamine transforms the glycosylated Ser and Thr residues into stable methylamine derivatives with a mass increment of +13 Da relative to nonglycosylated Ser and Thr residues. Peptide sequencing based on partial acid hydrolysis followed by mass spectrometric analysis or in favorable cases by CID-MS/MS enables the determination of the formerly O-glycosylated sites.     

Strategies and data precision requirements for the mass spectrometric determination of structures from combinatorial mixtures

Mass spectrometric data can be obtained for compounds in bead-bound combinatorial mixtures by several techniques. However, little specific information is available regarding (1) how well these data differentiate between candidate structures in large combinatorial pools, (2) what precision of data is required to achieve adequate specificity in these analyses, and (3) what are the best strategies for applying these data. In this work, computer modeling is used to address these questions. Strategies employing multiple filters (i.e., those that differentiate possible structures using more that one measured mass spectral parameter) are found to provide better specificity and to be more robust (that is, the specificity is less dependent on the precision of the data) than discrete filters. With moderate precision data (e.g., 50 ppm mass precision, 10% isotope ratio precision), multiple filter strategies are found to give unequivocal results for ～80% of the populations of combinatorial mixtures with most of the remaining degeneracy at the 2-fold level. A simple protocol for the application of multiple filter methods is presented.     

Mass spectrometric analysis of mercury incorporation into proteins for X-ray diffraction phase determination

Heavy-atom incorporation is an essential and often rate-limiting step in the determination of phases for X-ray diffraction studies of protein structures. Until the present, there has been no practical method (short of the X-ray diffraction experiment itself) to judge the success and extent of incorporation. Here we show that mass spectrometry is an effective tool for determining the extent of heavy-atom incorporation in proteins. In particular, we demonstrate the utility of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) for assaying mercury derivatization of cysteinyl thiol groups in proteins. Each of these mass spectrometric methods has advantages and drawbacks. ESI-MS provides a more accurate quantitative measurement of the extent of mercury incorporation, while MALDI-MS provides a useful lower limit to the level of mercury incorporation. Conversely, MALDI-MS does not require removal of excess derivatization reagents, salts and buffers, thus permitting facile analysis of single protein crystals as well as rapid, semiquantitative evaluation of the extent of protein mercuration. The approaches described in the present paper have contributed to the successful X-ray analyses of several noteworthy protein structures.     

The development of a method for the preparation of large amounts of 234Th-purified 238U-oxide

High purity ²³⁸U-oxide in amounts up to 60 g is required for capture cross-section measurements. The material needs to be purified for the ²³⁴Th daughter of ²³⁸U in order to reduce the natural γ background. It has been shown that 60 g of U₃O₈ can be purified by cation-exchange and retransformed in U₃O₈ in about 20 h. When the target is ready for use the ²³⁴Th content is 2% of the saturation value.     

Mass spectrometric imaging of lipids in brain tissue

The spatial distributions of various specific lipids in freeze-dried mouse brain sections were monitored using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Mouse brain sections were prepared by cryosectioning, rinsing in 0.15 M NH3HCOO, and freeze-drying, after which the samples were analyzed directly by TOF-SIMS, using Au3+ ions as primary ions. Positive and negative TOF-SIMS spectra of the tissue surface contained peaks from quasimolecular ions of a variety of specific lipids, including cholesterol, sulfatides, phosphatidylinositols, and phosphatidylcholines. Images showing the spatial signal intensity distributions of specific ions were recorded across analysis areas ranging from 100 x 100 microm(2) to 9 x 9 mm(2). The results demonstrate a highly complementary localization of cholesterol and phosphatidylcholine over dimensions from millimeter to micrometer range. Characteristic spatial distributions of several other lipids, including sulfatides and phosphatidylinositols, were observed. Principal component analysis was used to localize regions of the sample surface that show common spectral features. Spectra from different such regions showed large variations in lipid ion signals, indicating large variations in the lipid composition in different regions.     

Mass spectrometric determination of oxygen at partial pressures of less than 1.5 μPa (10−8 torr)

During an investigation of chemisorption and photodesorption reactions between oxygen and thin films of zinc oxide, the need arose for the determination of oxygen partial pressures in the range 1 μPa to 100 pPa (10^?8 to 10^?12 torr), in a static system, using a residual gas analyzer. Within this range the pumping actions for various components of the vacuum system were significant and this paper describes these actions and the techniques developed to lower the limit of detection of oxygen by mass spectrometric analysis to about 700 pPa .l (5 × 10^?12 torr .l)     

Determination of 238U, 234U, 232Th, 228Th, 228Ra, 226Ra and 210Pb concentration in excreta samples of inhabitants of a high natural background area

The high concentration of uranium and thorium in certain Brazilian areas provides an opportunity to evaluate the radiation exposure due to intake of radionuclides by the populations that live and work in areas with a high natural radiation background. Buena, where this study was conducted, is a small village on the coast in the northern part of Rio de Janeiro State, characterised by the presence of a large deposit of monazite sand. In this paper, the concentrations of 238U, 234U, 232Th, 228Th, 228Ra, 226Ra and 210Pb in faecal samples from inhabitants of this area were determined by a sequential analytical method. The results of the average concentrations in faeces of inhabitants of Buena are 9.4 +/- 3.4 mBq g(ash)(-1) for 238U, 9.2 +/- 4.0 mBq g(ash)(-1) for 234U, 7.0 +/- 4.2 mBq g(ash)(-1) for 232Th, 256.1 +/- 134.6 mBq g(ash)(-1) for 228Th, 335.5 +/- 192.8 mBq g(ash)(-1) for 228Ra, 156.6 +/- 74.1 mBq g(ash)(-1) for 226Ra and 66.7 +/- 17.7 mBq g(ash)(-1) for 210Pb. The results were compared with background concentrations from faecal samples from individuals living in Rio de Janeiro City. For most of the radionuclides analysed, the average concentration in faeces from inhabitants of the high natural radiation background was higher than the concentration found in Rio de Janeiro, considered a 'normal' background area.     

Mass spectrometric studies of impurities in gallium arsenide crystals

Techniques for the investigation of impurities in gallium arsenide crystals using mass spectrometry are described. The results obtained show a fair correlation with electrical measurements. Flat-bottomed etch pits are found which can be correlated with the oxygen content.The use of silica, boron nitride, alumina, and vitreous carbon crucibles is shown to contaminate the crystals. For crystals grown from silica crucibles, the silicon content decreases rapidly with increasing arsenic pressure during growth. From the distribution of impurities along the lengths of crystals, a number of distribution coefficients have been estimated.     

Mass spectrometric tracer pulse chromatographic investigations of eluent sorption with bonded RPLC packings

The experimental technique of mass spectrometric tracer pulse chromatography was used to investigate the uptake of RPLC eluents by a C 18-bonded packing. The experiments were carried out with eluents consisting of binary aqueous mixtures with acetonitrile, methanol, and tetrahydrofuran over the full range of eluent composition at 25 degrees C. The primary experimental data obtained were excess volumes of sorption for the eluent components. The excess volume data were then used to determine the absolute volume of each eluent component in the stationary phase as a function of composition. The absolute volumes were calculated by utilizing a series of strategies specific to limited eluent composition range. The linear inflection region of the excess volume isotherms was used to calculate the volume and composition of the eluent in the stationary phase for organic-rich eluents. Three different assumptions were used and evaluated for the water-rich eluent compositions. The assumptions were (i) constant volume of the sorbed layer, (ii) constant amount of water sorbed, and (iii) no water sorption. The latter assumption was adopted as the most satisfactory. The calculated void volume data were compared with the retention volume of thiourea and uracil, commonly used dead time markers. Neither thiourea nor uracil proved to be an accurate measure of the kinetic void volume.     

The development of an NMR spectrometer for the precision determination of the ratio of the resonance frequencies of nuclei

A nuclear magnetic resonance (NMR) spectrometer for determining the resonance frequencies of various nuclei at a magnetic field induction of 2.142 T is described. The spectrometer enables the NMR frequency of a nucleus to be recorded simultaneously with the frequency of the signal from a comparison nucleus and enables the magnetic field to be stabilized using the NMR signal from a third nucleus. The ratios of the resonance frequencies of protons and of the lithium-7 nuclei: F(H₂O)F(⁷Li) = 2.573041789(3) are obtained for a solution of lithium chloride in water, and also the ratio for protons and deuterons of an isotopic solution of water: F(H₂O)/F(D₂O) = 6.514399603(2). Methods of determining the systematic errors which occur when there are quadratic gradients of the magnetic field in the sample when processing spectral numerical data matrices are discussed.